1. Field of the Invention
The present invention relates to an actuator that makes it possible to drive a pump mechanism by using a pump-driving section and operate a displaceable member of a driving mechanism movably back and forth under the action of a pressure fluid supplied from the pump mechanism.
2. Description of the Related Art
An actuator, which is driven by the aid of a pressure fluid (for example, pressure oil), has been hitherto used, for example, in order to transport a workpiece and/or position the workpiece.
For example, a hydraulic actuator, which is disclosed in Japanese Laid-Open Patent Publication No. 2003-139108, comprises, for example, a motor which is driven and rotated by a current, a hydraulic pump which discharges the operation oil under the driving action of the motor, a piston which is displaceable in the axial direction with the aid of the operation oil, and a rod. The hydraulic pump is connected to the hydraulic actuator via pipes. The pipes comprise a first pipe for connecting the hydraulic pump and a port disposed on the side of the head of the hydraulic actuator, and a second pipe for connecting the hydraulic pump and a port disposed on the side of the rod of the hydraulic actuator.
When the motor is driven and operated, the operation oil is supplied from the hydraulic pump via the first pipe or the second pipe to the side of the head or the rod of the hydraulic actuator. The piston and the rod are displaced in the axial direction of the hydraulic actuator under the pressing action of the operation oil supplied into the hydraulic actuator. A pressure-adjusting mechanism, which suppresses the increase in pressure when the operation oil contained in the second pipe expands, is provided at an intermediate position of the second pipe.
It is assumed that the hydraulic actuator as described above is used in a way that depends on the shape of the workpiece and the situation, and is controlled by adjusting the output, such as the displacement speed of the piston and the rod, when the workpiece is moving or being positioned.
However, in the case of the hydraulic actuator, the operation oil is supplied from the hydraulic pump via the first pipe or the second pipe to the head or the rod of the hydraulic actuator. The pressure-adjusting mechanism, which is provided at the intermediate position of the second pipe, only absorbs increases in the operation oil when the pressure in the second pipe increases, as the piston and the rod are displaced.
That is, it is impossible to adjust the flow rate of the operation oil to be supplied from the hydraulic pump to the hydraulic actuator. Therefore, it is difficult to highly accurately adjust the displacement speed when the piston and the rod are displaced. For example, it is impossible to conform to the shape of the workpiece and the situation of the use of the hydraulic actuator when the workpiece is in motion.
Further, the hydraulic actuator and the hydraulic pump for supplying the operation oil are connected via first and second externally disposed pipes. Therefore, it is difficult to connect the first and second pipes. Further, the entire actuator is large in size, and hence requires a large installation space.